This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-076975, filed Mar. 17, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to an image forming apparatus such as a facsimile device and copying machine, and more particularly to a sheet feeder for taking out a recording sheet from a sheet storage cassette which is detachably attached to the image forming apparatus.
In recent years, most facsimile devices are capable of printing images on recording sheets of plain paper previously cut into a preset size. A typical one of the facsimile devices includes a sheet storage cassette for storing a stack of recording sheets, a cassette attachment port formed in the side wall of a case of the facsimile device to detachably attach the sheet storage cassette thereto, a sheet feeding mechanism for taking out recording sheets one by one from the sheet storage cassette attached to the internal place of the cassette attachment port, and a printing unit for printing an image on the recording sheet fed by the sheet feeing mechanism in an electrophotographic process.
The sheet storage cassette generally includes a sheet tray having a preset depth, a supporting plate which supports the recording sheets received in the sheet tray and is rotatable about one end thereof to allow movement of the other end to the open plane of the sheet tray, a spring member for pushing up the supporting plate by elastic force, a hooking member for hooking the supporting plate pushed down against the elastic force of the spring member, and a releasing member for releasing the hooking member when the sheet storage cassette is attached to the internal place of the cassette attachment port. The sheet feeding mechanism includes a pickup roller arranged above the sheet storage cassette attached to the internal place of the cassette attachment port so as to face the other end side of the supporting plate of the sheet storage cassette and a driving unit for driving the pickup roller. The pickup roller is mounted on a roller shaft rotatably supported by a pair of bearing holes formed in the side walls of the case of the facsimile device. The user puts a stack of recording sheets on the supporting plate of the sheet storage cassette, pushes down the supporting plate together with the recording sheets, and then inserts the sheet storage cassette into the cassette attachment port in a state where the recording sheets are fully received within the sheet tray of the sheet storage cassette. When the sheet storage cassette is attached to the internal place of the cassette attachment port, the releasing member releases the hooking member so as to cause the uppermost one of the recording sheets to abut against the pickup roller. Therefore, when the pickup roller is rotated by the driving force of the driving unit, the uppermost recording sheet is taken out from the sheet storage cassette and fed to the printing unit.
Conventionally, the cassette attachment port is formed in the side wall which lies in the same plane as one of the bearing holes in some cases in order to horizontally attach and detach the sheet storage cassette in a direction perpendicular to the sheet feeding direction of the sheet feeding mechanism. In this case, the bearing holes are arranged above the cassette attachment port and a distance between the bearing hole and the cassette attachment port is set large so that the strength of the side wall of the case will not become insufficient for holding the roller shaft supported by the bearing hole.
However, the above construction tends to cause a problem when recording sheets are supplemented before the sheet storage cassette becomes completely empty. That is, if the sheet storage cassette having some recording sheets left received therein is withdrawn from the cassette attachment port, end portions of the recording sheet rise and are caught by the side wall between the bearing hole and the cassette attachment port and a sheet jam which makes it difficult to supplement recording sheets may occur in some cases. At this time, if an attempt is made to forcedly pull out the sheet storage cassette, the recording sheets may be separated from the sheet storage cassette or torn. In order to avoid this, it is necessary to withdraw the sheet storage cassette while manually holding down the recording sheets together with the supporting plate by use of a gap between the sheet storage cassette and the cassette attachment port. This is an extremely troublesome task for the user.
An object of this invention is to provide a sheet feeder capable of reliably preventing occurrence of a sheet jam caused when the sheet storage cassette having sheets received therein is withdraw from the cassette attachment port.
According to this invention, there is provided a sheet feeder comprising a sheet storage cassette for storing a stack of sheets and pushing up the sheets by elastic force; a case having a cassette attachment port through which the sheet storage cassette is detachably attached; and a feeding mechanism for feeding each of the sheets stored in the sheet storage cassette attached to an internal place of the cassette attachment port in a sheet feeding direction substantially perpendicular to an attachment and detachment direction of the sheet storage cassette; wherein the feeding mechanism includes a roller shaft disposed above the sheet storage cassette attached to the internal place of the cassette attachment port and extending in the attachment and detachment direction of the sheet storage cassette from a side wall of the case, a pickup roller rotated for taking out the uppermost one of the sheets stored in the sheet storage cassette attached to the internal place of the cassette attachment port, and a rise-spoiling member attached to the roller shaft, for spoiling a rise of the sheets when the sheet storage cassette is withdrawn from the cassette attachment port, the rise-spoiling member extruding downward to a position below an upper edge of the cassette attachment port and extending from the pickup roller to the vicinity of the side wall of the case.
In the above sheet feeder, the rise-spoiling member extrudes downward to a position below an upper edge of the cassette attachment port and extends from the pickup roller to the vicinity of the side wall of the case. That is, the rise-spoiling member holds down the sheets uniformly in a range from the pickup roller to vicinity of the side wall of the case when the sheet storage cassette is withdrawn from the cassette attachment port. As a result, the end portions of each sheet do not rise above the cassette attachment port, and are not be caught by the side wall of the case. Accordingly, occurrence of a sheet jam can be prevented.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.